Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$110.29	12.709%	$124.3068	$124.31	$124.30	$124.30
Purchase #2	$149.45	12.469%	$168.0849	$168.08	$168.10	$168.10
Purchase #3	$183.36	9.368%	$200.5372	$200.54	$200.55	$200.50
Purchase #4	$41.53	4.502%	$43.3997	$43.40	$43.40	$43.40
Purchase #5	$192.99	9.418%	$211.1658	$211.17	$211.15	$211.20
Purchase #6	$99.31	10.272%	$109.5111	$109.51	$109.50	$109.50
Purchase #7	$75.35	10.584%	$83.325	$83.33	$83.35	$83.30
7 purchase totals =	$852.28		$940.3305	$940.34	$940.35	$940.30